In the design of a twistlock fastener, one of the most important features is to have a very positive set of latching positions so that the user will know exactly at which of the positions the latching head is located.
Many of the prior art twistlock fasteners operate on the principle of its latching head acting against a resilient spring member, such as disclosed in U.S. Pat. Nos. 3,344,488; 2,382,943 and 1,190,582; British Patent No. 10,660; Swedish Pat. No. 176,401 and West German Patent No. 2,161,626. The difficulty with each of these prior art devices is that they do not provide a very positive latching arrangement.
One twistlock fastener that has been found to give a positive set of latching positions is disclosed in U.S. Pat. No. 4,498,827. Unfortunately, this fastening device has a very complex design requiring exact dimensional compliance between the latching member and the base member which is difficult to manufacture and assemble. Also, this patented structure does not perform as a one-quarter turn twistlock since it has three distinct settings for every one-quarter turn.
This invention is directed to a novel latch member that cooperates in a square-shaped aperture of the base member to provide a one-quarter turn twistlock fastener with very positive quarter turn latching positions. The simplicity of the design of this novel twistlock fastener makes it easy to manufacture and to assemble.